In the field of cryoablation (therapeutic destruction of tissue by the application of extreme cold), a refrigerant vaporizes at low pressure and low temperature in a boiling chamber of an ablation catheter or a surgical probe. A thermally conductive structure forming a cryoapplicator allows the heat-exchange of the refrigerant with the tissue. Cryoablation, cryotherapy or cryosurgery are established treatments for the controlled destruction of tissue by the application of extreme cold. Examples for application are the removals of warts or moles, the destruction of tumor for the treatment of liver, prostate and lung cancer, and the selective ablation of cardiac tissue for the treatment of arrhythmia.
Rigid metallic structures are in widespread use for cryoapplicators, particularly if the target area is a spot or point like region. Here, U.S. Pat. No. 6,629,417 and U.S. Pat. No. 6,182,666 describe systems for the treatment of skin and endo-cervical tissue. Devices for the focal ablation of cardiac tissue are described in U.S. Pat. No. 5,281,213, U.S. Pat. No. 5,423,807 and U.S. Pat. No. 6,589,234. A system for cooling very small portions of tissue to extremely low temperatures is described in U.S. Pat. No. 5,901,783.
If tissue is ablated along an elongated region more flexible structures are used. Here, bellows surface can maintain both heat conduction and flexibility as described by U.S. Pat. No. 6,241,722. WO 00/32126 describes the combination of flexible segments with low thermal conduction with rigid segments of high thermal conduction. Here, also methods for the realization of a varying thermal conduction along the circumference of a cryoapplicator (good thermal conduction to the target tissue while limiting the heat loss on the opposite side of the applicator) are described. Furthermore, the use of thin walled tubing or inflatable balloon like material for the realization of good heat conduction in a flexible structure is described in U.S. Pat. No. 6,602,247 and EP 1,430,849.
One example which may require the creation of an elongated lesion in cardiac tissue is the treatment of atrial fibrillation. Here, a catheter design containing a loop like cryo-applicator structure is described in EP 1,356,779 and U.S. Pat. No. 6,979,331. Another example is the treatment of atrial flutter by creating an elongated lesion in the area of the cavotricuspid isthmus area as described in PCT/EP2009/001804.
Furthermore, WO 2009/112269 discloses an ablation element for an ablation device, the ablation element comprising a tubular body defining an inner lumen. The tubular body comprises a core formed by a wound filament structure and comprises a mantle surrounding the core. The tubular body, particularly the mantle, is configured to have a spatially varying value of thermal conductivity along a circumference of the tubular body.
However, although the arrangement of WO 2009/112269 already provides a proper solution for the spatially dependent supply of a cooling medium to tissue, there is still room for improvement.